Control arrangement for magnetic circuit element



April 1967 A. L. WELLFORD CONTROL ARRANGEMENT FOR MAGNETIC CIRCUITELEMENT Filed June 26, 1963 FIG.|

INVENTOR. ARMISTEAD WELLFORD C/Mm mm ATTORNEY United States Patent Ofiice 3,314,002 Patented Apr. 11, 1967 Filed June 26, 1963, Ser. No. 290,856 1 Claim. (Cl. 323-51) This invention relates to magnetic devices. More particularly, it relates to means for variably adjusting the saturation flux density of the cores in saturablernagnetic circuit elements. v In many situations where magnetic circuit elements are used such as in magnetic coupled multivibrators, magnetic amplifiers, etc., the cores of these devices arechosen to be of the saturable type because of their inherent volt-second operating characteristic. It is often desired to vary the saturation flux density'of these cores. For example, in a magnetic coupled multivibrator, the output frequency is dependent upon the value of the applied voltage and the volt-second characteristic of the core of the magnetic coupling device therein, i.e., the saturable transformer. In such type of multivibrator, a constant frequency is produced if the applied voltage is maintained at a constant value. To change the output frequency of the multivibrator while maintaining the applied voltage at the same aforesaid value, it is generally, necessary to utilize a transformer having a core with a different volt-second characteristic. Similarly, in other volt-second devices such as saturable reactors and magnetic amplifiers, the core may also have to be changed to change the timing effect of the device if the respective voltages supplied to the device are maintained at a constant level.

If the saturation flux density of the core of a saturable magnetic circuit element couldbe varied to change its volt-second characteristic, then a great, variety of circuit operations wouldbeenabled such as the varyingof. the frequency of magnetic coupled multivibrators and controlling such frequency to finedegree, the varying of the timing effect of a saturable reactor suchas that used in a phase shifting device, and in many other situations in which the adjusting of the volt-second characteristic of the core of a saturable magnetic element in response to a given circuit phenomenon can be eflicaciously utilized. Accordingly, it is an important object of this invention to provide means for varying the saturation flux density of the core of a saturable ma-getic circuit element to thereby vary its volt-second characteristic.

Itis another object to provide 'means in accordance with the preceding object which enables the fine varying of such saturation flux density.

. Generally speaking an in accordance with the invention, there is provided means for varying the saturation flux density of a magnetic circuit element comprising means which produces a magnetic flux disposed adjacent tothe magnetic circuit element and adapted to be moved closerto, further away, and at diiferent flux axial orientations with respect to said magnetic circuit element;

The features of this invention which are believed to be new are set forth with particularity in the appended claims. The invention itself, however, may best be understood by reference to the following description when taken in conjunction with the accompanying drawings which uration flux density occurs therein.

show an embodiment of a means for varying the saturation flux density of a magnetic circuit element according to the invention.

In the drawings:

FIG. 1 is a diagram of a circuit illustrating the principles of the invention; and

FIG. 2 is a depiction of an illustrative embodiment of an arrangement constructed in accordance with the principles of the invention.

It has been found that when a circuit component whose operation depends upon the volt-second characteristic of a saturable magnetic care, such as the saturable transformer of a magnetic coupled multivibrator, is subjected to a steady state, i.e., a DC. magnetic flux, or to an A .C. magnetic flux, such as a synchronized A.C. flux, applied at right angles to the direction of the flux generated in the core of the magnetic circuit element, a decrease in sat- I In the case of the magnetic coupled multivibrator, this decrease in the saturation flux density of the core of the coupling saturable transformer therein results in the higher frequency operation of the multivibrator. It also has been found that if the core of a timing saturable reactor, such as a voltsecond device utilized to impart a phase shift to a voltage applied thereto, is subjected to such DC. or synchronized A.C. flux applied at right angles thereto, that its timing period decreases, the latter decrease also being due to the decrease in saturation flux density of the core.

A possible explanation for such decrease but to which it is not intended to be limited, is as follows: The core material of a magnetic circuit element consists of a num .ber of individual grains. Qualitatively speaking, regardless of the random orientation of these grains statistically, each grain saturates in a given amount of volt seconds in accordance with the total flux density that it is subjected to. Thus, if two separate fluxes are supplied to a grain, consequently, the resultant of the vector summation of these fluxes is the determining factor in the total flux density to which the grain is subjected. Thus, if there is again considered the saturable, transformer in a magnetic coupled multivibratonit is seen that a grain in the core :of this transformer during circuit operation thereof is subjected to the flux produced by the transformer windings. Now, if the grain is subjected to a second flux source whose direction of flux is at right angles to the direction of the flux produced by the transformer windings and if it is further assumed that the transformer winding flux is a horizontal vector and that the second flux is a vertical vector, then in the operation of the multivibrator, the horizontal vector reverses direction each half cycle while maintaining the same length. If the second flux source is a steady state flux, i.e., resulting from a direct current, or produced by a permanent magnet, the vertical vector remains unchanged so that the resultant in each half cycle of the multivibrator is longer than either of the individual flux vectors, but it is of the same length during each half cycle of the output from the multivibrator. If the second flux source is produced by an alternating current whereby it changes direction every half cycle in accordance with such alternating current, and if this second flux is synchronized with the AC. flux produced due to the transform-er windings in the multivibrator, then the vertical vector changes direction each half cycle but the resultant vertical vector is the same length each half cycle. Thus,

if the second flux source in the example is an A.C. flux synchronized with the AC. output of the multivibrator, then the multivibrator will still produce symmetrical operation but at an increased frequency since the saturation flux density of the core of its transformer has been decreased due to the second flux source.

In FIG. 1, there is shown an example of this invention wherein a steady state magnetic element is used as a second, i.e., biasin-g flux source for the core of :a saturable transformer. Such biasing flux source is depicted in FIG. 1 as a permanent magnet. However, it is readily appreciated that it may be an electromagnetpowered by a D.C. source. The direction of the flux produced by the permanent magnet as depicted in FIG. 1 is at right angles to the "flux produced by the toroidal core because of the elfect of the transformer windings thereon.

In the circuit of FIG. 1, the output of an AC. source is applied tothe primary winding 18 of a saturable transformer 16 through a current limiting resistor 12 and a bridge rectifier comprising diodes 13, 15, 17 and 19.

The cathode to anode path of a breakdown diode 14 is connected between the junction of diodes 13 and 19', and the junction of diodes 15 and 17. With this arrangement, an alternating current potential clamped to a predetermined amplitude appears in transformer 16. A permanent magnet 22 is disposed in an orientation such that the direction of the flux produced thereby is at right angles to the flux produced by the windings of transformer 16 in core 21.

It has been found that the saturation flux density of core 2 1 with permanent magnet 22 disposed as described hereinabove is less than its saturation flux density when permanent magnet 22 is not utilized. As permanent magnet 22 is rotated such that the direction of its flux varies from a right angle to a parallel direction with respect to the direction of the flux produced in core 21, the saturation flux density of core 21 'varies from a minimum saturation fiux density to a maximum saturation flux density, the latter being substantially equal to its saturation flux density when permanent magnet 22 is not present. Thus, the use of the second flux source, as depicted by the permanent magnet example in FIG. 1, functions to enable the fine trimming of the saturation flux density of core 21 and thereby correspondingly vary its volt-second characteristic. In the circuit of FIG. 1, this is evidenced by the control of average voltage as measured across load resistor 23.

It is thus seen that in accordance with the principles of this invention, a second magnetic flux source, either D.C. or AC. or permanent magnet could be used to vary the frequency of a magnetic coupled multivibrator utilized as the frequency determining element in a static inverter to provide fine precise voltage regulation of the output thereof Such second flux source could be used to provide a biasing magnetic sign-a1 to static inverters contained in a parallel arrangement of such inverters to effect load division between the parallel inverters, since such load division is effected by regulating frequency.

Clearly, it could be utilized with any volt-second device to finely vary its timing.

To enable a variation swing in saturation flux density in a magnetic circuit element, the direction of the biasing flux source could be placed at a 45 angle to the circuit element and, then, it could be rotated to a 90 position to provide an upper limit to a variation swing and to a parallel position to provide a lower limit to the variation swing.

The amount of variation which can be accomplished by the biasing in addition to being a function of its direction is also a function of its magnitude and the amount of its spacing from the magnetic circuit element being biased thereby. Thus, in the circuit of FIG. 1, a decrease in saturation flux density in core 21 varies directly with the increase in the fiux produced by biasing source 22 and inversely with the distance that source 22 is spaced from core 21.

In FIG. 2 there is shown an illustrative embodiment of a permanent magnet flux biasing arrangement constructed in accordance with the principles of this invention. The illustrative saturable circuit element to be biased is chosen in FIG. 2 to be a saturable transformer comp-rising a toroidal core 24 and having a winding 26, adapted to be connected to a utilization circuit by leads 25 and 27, is contained in a housing 30 consisting of nonmagnetic material, suitable a laminated material such as epoxy glass laminate, and which suitably may have a parallelepiped configuration although the shape of the housing is not material. The magnetic circuit element whose saturation flux density is to be varied with, as toroidal core 24 consisting of a magnetic material is disposed inthe housing and the remaining portion of the interior housing is filled with an insulating material such as potting compound. A portion 34 of a front wall 32 of housing is cutout to expose a portion of the flat surface of core 24. A flat plate 36 suitably consisting of the same material as housing 30 and having a pair of parallel disposed slots 38 and 40 has mounted on its under surface a permanent magnet 42 which preferably may be a channel horseshoe permanent magnet, the base of the U having a width substantially equal in length to the base of cutout portion 34, plate 36 having a width such that it may be received between tabs extending from upper surfaces of side walls 33 and 35 of housing 30.

The term channel horseshoe signifies that the permanent magnet is cut from long bars with a U-shaped cross-section. These bars are similar in shape to structural steel channels.

Plate 36, when in position on housing 30 may be moved slideably back and forth along the front to rear axis of housing 30' whereby the legs of permanent magnet 42 may vary a distance from the exposed surface of core 24 from substantially zero to a given maximum amount. A pair of screws are received in slots 38 and 40 when plate 36 is in position on housing 30, these screws and the lengths of the slots determining the extent and limits of motion permitted of'plate 36.

Preferably that portion of core 24 which is exposed and adapted to be subjected to the flux produced by permanent magnet 42 has neither insulation nor winding turns thereon whereby the reluctance gap between core 24 and permanent magnet 42 can be reduced substantially to zero. Permanent magnet 42 may suitably consist of a material such as Alnico V whereby it produces a very high external energy per pound. The use of a channel horseshoe or horseshoe magnet gives a maximurit flux change per pound of permanent magnet materia In the operation of the arrangement of FIG. 2, magnetic flux produced from permanent magnet 42 enters the edges of the laminations of core 24 and flows within the curved planes formed by each lamination before returning to the opposite pole of the permanent magnet. At least a portion of this path is parallel to the flux produced by the excitation of the Winding 26 of the core itself.

Although it would appear that asymmetrical operation would result due to the parallel unidirectional flux from the permanent magnet, this is not the case. Actually the permanent magnet operates in a manner such that it reduces the effective iron cross-section of the magnetic circuit element and, therefore, maintains symmetrical operation. Such position has been found to give the maximum change in volt-second capacity in comparison to other positions of the permanent magnet.

While there have been described What are considered to be the preferred embodiments of this invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing form the invention and it is, therefore, aimed in the appended claim to cover all such changes and modifications as fall within the scope of the invention.

What is claimed as new and desire-d to be secured by Letters Patent of the United States is:

Means for varying the flux of the core of a magnetic circuit element comprising a housing consisting of a nonmagnetic material for containing said circuit element, said housing comprising a first flat surface having a cutout portion, a member having a second flat surface, a permanent magnet afiixed to said surface, said second flat surface being adapted to be moved along said first flat surface with said magnet received in said cutout portion such that the direction of the flux produced thereby is at right angles to the flux produced by said circuit eleaway from said core in said right angle flux direction by movement of said second surface.

References Cited by the Examiner UNITED STATES PATENTS JOHN F, COUCH, Primary Examiner. LLOYD MCCOLLUM, Examiner.

ment, said magnet being moved closer to and further 15 W. E. RAY, Assistant Examiner. 

